Many types of devices have been developed over the years for the purpose of converting liquids into aerosols or fine droplets readily converted into a gas-phase. Many such devices have been developed, for example, to prepare fuel for use in internal combustion engines. To optimize fuel oxidation within an engine's combustion chamber, the fuel must be vaporized, homogenized with air, and in a chemically-stoichiometric gas-phase mixture. Ideal fuel atomization and vaporization enables more complete combustion and consequent lower engine out pollution.
More specifically, relative to internal combustion engines, stoichiometry is a condition where the amount of oxygen required to completely burn a given amount of fuel is supplied in a homogeneous mixture resulting in optimally correct combustion with no residues remaining from incomplete or inefficient oxidation. Ideally, the fuel should be completely vaporized, intermixed with air, and homogenized prior to ignition for proper oxidation. Non-vaporized fuel droplets do not ignite or combust completely in conventional internal and external combustion engines, which degrades fuel efficiency and increases engine out pollution.
Attempts to reduce or control emission byproducts by adjusting temperature and pressure typically affect the NOx byproduct. To meet emission standards, these residues must be dealt with, typically requiring after treatment in a catalytic converter or a scrubber. Such treatment of these residues results in additional fuel costs to operate the catalytic converter or scrubber and may require additional component costs as well as packaging and mass implications. Accordingly, any reduction in engine out residuals resulting from incomplete combustion would be economically and environmentally beneficial.
An engine running a closed loop in which λ=1 (e.g., when λ equals the ratio of air/fuel ratio (AFR) divided by the stoichiometric air/fuel ratio (AFRstoich) is targeted will typically be operating at or near stoichiometery. If the fuel is not completely vaporized, the engine management system (EMS) will add extra fuel to ensure that stoichiometery is reached as the oxygen sensor is monitoring excess oxygen in the exhaust. A reduction in efficiency caused by fuel not being completely vaporized results from extra fuel being added to ensure stoichiometery is achieved. Fuel energy is wasted and unnecessary pollution is created when the fuel is not completely vaporized. Thus, by further breaking down and more completely vaporizing the fuel-air mixture, better fuel efficiency may be available.
Many attempts have been made to alleviate the above-described problems with respect to fuel vaporization and incomplete fuel combustion. In automobile engines, for example, inlet port or direct fuel injection systems have almost universally replaced carburetion for fuel delivery. Fuel injectors spray fuel directly into the inlet port or cylinder of the engine and are controlled electronically. Injectors facilitate more precise metering and control of the amount of fuel delivered to each cylinder independently relative to carburetion. This reduces or eliminates charge transport time facilitating optimal transient operation. Nevertheless, the fuel droplet size of a fuel injector spray is not optimal and there is little time for the fuel to mix with air prior to ignition.
Other prior systems, such as heated injectors and heated fuel rails have also been developed in attempts to remedy the problems related to fuel vaporization and incomplete fuel combustion.
Most fuel delivery systems require a source of air as part of delivering and/or preparing the fuel for delivery to a combustion chamber. A number of challenges exist in providing the source of air under proper conditions.